Currently, the International Telecommunication Union-Radiocommunication sector (ITU-R) is developing a vision of various convergence services based on a 5G network. Also, the South Korean government established a development strategy for the future mobile communication industry in January 2014, and selected a social network service (SNS), mobile three-dimensional (3D) imaging service, intelligent service, super high-speed service, and ultra high-definition (UHD) imaging/hologram service as five key services.
In addition, the European Union, China, Japan, South Korea, etc. established a task force for discussing a 5G network and service, and are discussing a user-oriented 5G service reflecting the lifestyle of 2020, which is the target time of commercializing 5G, in tandem with an innovation of mobile communication technology for providing an ultra high transmission rate of gigabytes per second to users.
Internationally, 5G requirements and technology standards have not yet been determined, but the requirements are expected to be determined for about five different aspects.                Ultra high speed & low latency: 1000 times higher speed than Long Term Evolution (LTE), a ultra-low latency response time of less than a few milliseconds, and realistic content        Massive/seamless connectivity: accommodation of 1000 times more devices and traffic, and ensuring seamless connectivity        Intelligent/flexible network: provision of a software-based structure, real-time data analysis, and intelligent/personalized services        Reliable/secure operation: network availability/reliability of more than 99%, and self-healing/reconfiguration        Energy/cost-efficient infrastructure: 50 to 100 times higher energy efficiency than LTE, and a reduction in the cost of infrastructure/devices        
Meanwhile, in 5G mobile communication, a study is being conducted on the use of a millimeter wave band in which it is easy to ensure a continuous wide bandwidth of a minimum of 500 MHz or more, for example, extremely high frequency (EHF) bands of 27 to 29 GHz and 70 to 80 GHz, but an agreement has not yet been reached. In these EHF bands, it is possible to highly increase the density of antennas. Therefore, when the physical size of an antenna is determined, the interval between radiators constituting an antenna is reduced with an increase of a frequency, and thus an increased number of radiators can be included.
A plurality of radiators serve as the hardware basis of 3D beamforming technology for generating antenna beams in various shapes by controlling the magnitude and the phase of a radio frequency (RF) signal and massive multiple-input multiple-output (MIMO) technology which enables multiple transmissions. In this way, it is expected that the 3D beamforming technology for configuring an optimal RF environment and performing high-speed transmission by controlling electric field strength vertically or horizontally according to the distribution of users or by forming several beams and beam switching/tracking technology for providing an optimal link by selecting an optimal beam from among several beams or by changing the beam direction of an antenna according to the location of a user will be actively applied to 5G mobile communication.
FIG. 1 is a diagram showing a configuration of a base station that is applicable to 5G mobile communication. As shown in FIG. 1, a mobile communication cell managed by one base station can be divided into three sectors A, B, and C. Each sector can be divided into a plurality of, for example, 16, beam spots, and RF modules, which have beam antennas to process an analog signal, which can be configured to correspond to the beam spots, on a one-to-one basis.
FIG. 2 shows a connection relationship between MACs and modems in 5G mobile communication. As shown in FIG. 2, according to 5G mobile communication, a total of 16 beam spots dividing each sector of a mobile communication cell correspond to RF modules which have beam antennas to process an analog signal on a one-to-one basis. The RF modules correspond to modems which perform baseband signal processing, for example, channel coding/decoding, digital modulation/demodulation, multi-antenna processing, and generation of an orthogonal frequency division multiplexing (OFDM) signal, on a one-to-one basis, and the modems also can correspond to MACs which perform mapping between logical channels and transmission channels, error correction, and distribution of time and frequency resources to a plurality of pieces of UE on a one-to-one basis.
Assuming that the modems which correspond to the beam spots on a one-to-one basis also correspond to the MACs on a one-to-one basis as indicated by dotted lines in FIG. 2, there may be a relatively large amount of UE traffic at a specific beam spot, whereas there is a relatively small amount of UE traffic at other beam spots. In this case, there is no way to distribute the large amount of UE traffic, and thus an MAC managing the beam spot at which the large amount of UE traffic is concentrated provides degraded service quality due to a lowered processing speed.
This work was supported by the Giga KOREA project of MSIP/Giga KOREA Foundation, Republic of Korea. [GK14N0100, Development of millimeter wave-based 5G mobile communication system]